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resulting from electron transfer through the DNA to intercalated
AQMS is readily distinguished from that of AQMS on the electrode
surface. The difference in the chemical environment between
free and intercalated AQMS greatly affects its reduction potential,
allowing monitoring of DNA hybridization in real time. In another
study, Gorodetsky
et al.
[41] utilized DNA duplexes functionalized
withpyrenetofabricateDNA-modifiedelectrodesonhighlyoriented
pyrolytic graphite (HOPG). The reduction of DNA-bound intercala-
tors was observed as a consequence of a DNA-mediated reaction.
The reduction of the intercalator was attenuated in the presence of
thesingle-basemismatches,CAandGT,independentofthesequence
composition of the ODN. Sensitivity to single-base mismatches
is enhanced when methylene blue reduction is coupled in an
electrocatalytic cycle with ferricyanide. Furthermore, utilization of
HOPG as electrode material allowed authors to investigate the
electrochemistry of previously inaccessible metallointercalators,
[Ru(bpy)
2
dppz]
2
+
and [Os(phen)
2
dppz]
2
+
, at the DNA-modified
HOPG surface. It was shown that HOPG presents a suitable and
reproduciblesurfaceforelectrochemicalDNAsensorsexploitingthe
charge transport properties of DNA. Again, Gorodetsky
et al.
shown
that DNA-mediated electrochemistry can promote reactions at a
distanceontheDNAsugar-phosphatebackbone[42].Itwaspointed
out that relative current densities for DNA-mediated disulfide
reductions of 1.8
μ
A/cm
2
differed significantly from that for well
stacked intercalator reduction of about80
μ
A/cm
2
.
7.3.3
Hybridization Indicators, Intercalators and Groove
Binders
VariousmoleculesarecapabletobindtotheDNAduplexortosingle-
stranded DNA. The application of DNA binding molecules for the
detection of base-pair mismatches is discussed below. For instance,
Millan
et al
. demonstrated sequence-selective electrochemical DNA
sensing using hybridization indicators [9]. In this detection scheme,
DNA capture strands were covalently immobilized on a glassy
carbon 14 electrode and [Co(bpy)
3
]
3
+
and [Co(phen)
3
]
3
+
served
as hybridization indicators that display reversible redox behavior.
Presumably, electrostatic interactions with the negatively charged
